1. Field of the Invention
The present invention relates to an exhaust silencer of an internal combustion engine used for construction equipment and the like and a communicating pipe thereof.
2. Description of Related Art
An exhaust silencer called a "muffler" is connected to an exhaust pipe of an internal combustion engine used for a construction equipment etc. for reducing exhaust noise from a combustion chamber.
Conventionally, various arrangements are known for the exhaust silencer. In an internal combustion engine of construction equipment, a multistage-expansion type in which sound is damped by repeating contraction and expansion of exhaust gas and a resonant type in which the exhaust gas is resonated for damping sound are known as conventional examples of the exhaust silencer.
A conventional example of the multistage-expansion type exhaust silencer is shown in FIG. 15.
In FIG. 15, the conventional exhaust silencer 100 has three partitions 52A to 52C aligned in an axial direction for partitioning an inside of a drum-shaped body 51 into four chambers 51A to 51D, a communicating pipe 53 supported by the partitions 52A to 52C coaxially with the body 51, an inlet pipe 54 with an end and intermediate portion thereof being secured to the body 51 to face the uppermost-stream chamber 51A, and an outlet pipe 55 with an end and intermediate portion thereof being secured to the body 51 to face the lowermost-stream chamber 51D.
Among the partitions 52A to 52C, a large opening 52D to intercommunicate adjacent chambers is formed on the partitions 52A and 52C supporting both end sides of the communicating pipe 53. Both ends 53A of the communicating pipe 53 respectively facing the first chamber 51A and the fourth chamber 51D is closed, and a large number of communicating hole 53B is formed on a circumference of the communicating pipe 53.
An end 54A of the inlet pipe 54 is closed and a plurality of communicating hole 54B is formed on a circumference of the communicating pipe 54. The outlet pipe 55 has a plurality of communicating hole 55B and an end being open to the air.
Flow of the exhaust gas sent from the outlet pipe is straightened in radial direction by the communicating holes 54B of the inlet pipe 54 and is sent to the first chamber 51A, and the exhaust gas is damped by being sent from the first chamber 51A to the second chamber 51B through the opening 52D. Subsequently, the exhaust gas flows to inside of the communicating pipe 53 through the communicating holes 53B, circulates with angle thereof being changed into an axial direction, and is sent to the third chamber 51C through the communicating holes 53B. Further, the exhaust gas is sent from the third chamber 51C to the fourth chamber 51D through the opening 52D to flow into the outlet pipe 55 through the communicating holes 55B, which is discharged into the air.
Accordingly, the circulating exhaust gas repeatedly experiences total of four contractions and expansions by the two openings 52D and the two communicating holes 53B, thereby conducting so-called multistage-expansion type damping. Especially, the exhaust gas passes a predetermined length (a predetermined time) in the communicating pipe 53 while being contracted without full expansion, thus experiencing effective damping effect.
However, following disadvantage occurs in the multistage-expansion type exhaust silencer.
Though the opening 52D for contracting the exhaust gas is formed on the partitions 52A and 52C for dividing adjacent chambers, sufficient damping effect cannot be obtained when the opening area of the opening 52D is large.
More specifically, the opening 52D is an opening formed on the partitions 52A and 52C and there is only small length in the gas flow direction. Accordingly, rectification effect is deteriorated when the opening are is enlarged in accordance with increase in flow velocity of the exhaust gas.
Accordingly, when the rectification effect is lowered by enlarging the opening 52D of the respective partitions 52A and 52C in the conventional example, though there are apparently four damping chambers (the first chamber 51A to the fourth chamber 51D), only two practically effective damping chambers, i.e. upstream chamber and lower-stream chamber provided on both sides of the central partition 52B, can be established, which deteriorates noise reduction effect.
A conventional example of resonant type exhaust silencer will be described below.
Generally, the resonant type exhaust silencer has a plurality of chamber inside drum-shaped body divided by partitions, a part of the plurality of chambers being a resonant chamber for damping the exhaust noise.
For example, the resonant chamber is formed on a position between two damping chambers. A communicating pipe stretches over the two damping chambers sandwiching the resonant chamber and passes through the resonant chamber. An intermediate portion of the communicating pipe is exposed to the resonant chamber, and a large number of communicating holes are formed on a circumference of the intermediate portion to intercommunicate an inside of the communicating pipe and an inside of the resonant chamber.
A substantial part of the exhaust gas sent from the upstream damping chamber is sent to the lower-stream chamber through the communicating pipe and the rest is sent to the resonant chamber through the communicating holes. The exhaust gas (pressure wave thereof) reflects in the resonant chamber to reduce energy thereof especially on a resonant range thereof. The exhaust gas returned from the resonant chamber to the communicating pipe by pulsation etc. joins the exhaust gas flowing toward the lower-stream dumping chamber.
However, following problems occur in the resonant type exhaust silencer.
First, only specific frequency of the exhaust noise is damped in the resonant chamber and noise reduction for the entire range of the exhaust noise cannot be expected.
Since the resonant chamber has to be tuned for each type of the internal combustion engine, which complicates design and deteriorates at none-tuned frequency.
Further, since a large space is required for the exhaust silencer to have the resonant chamber, the size of the exhaust silencer itself has to be made large.
A combination of the above multistage-expansion type and the resonant type has been developed.
Since the ordinary multistage-expansion type exhaust silencer alternately circulates the exhaust gas between the inside of the pipe and the damping chamber through a pipe hole to damp the exhaust noise, resistance is caused to raise backpressure by repeating contraction and expansion of the exhaust gas passing the pipe hole.
To solve the above disadvantage, a control valve has been used for controlling the backpressure (Japanese Patent Laid-Open Publication No. Hei 11-22444).
Though the above arrangement is basically a multistage-expansion type having a plurality of damping chamber inside a cylindrical shell, a communicating pipe passing through, for instance, three damping chambers are provided, and a controllably openable control valve is provided inside the communicating pipe to a position corresponding to an intermediate chamber.
At low engine speed, the control valve is closed to shut the communicating pipe. Accordingly, the exhaust gas passing the communicating pipe enters into the intermediate damping chamber from upstream side relative to the control valve and is discharged to lower-stream side of the communicating pipe relative to the control valve. In other words, the intermediate damping chamber functions as a multistage-expansion type exhaust silencer, so that damping effect can be improved.
On the other hand, the control valve is opened at high engine speed to release shutting of the communicating pipe. Accordingly, a part of the exhaust gas passing the communicating pipe directly flows into the lower-stream damping chamber and another part enters into and go out of the intermediate damping chamber, so that the intermediate damping chamber works as a resonant chamber. Accordingly, damping effect by the resonant chamber can be obtained while largely reducing the exhaust resistance at the communicating pipe.
However, there can be following disadvantage in the above arrangement.
Though pressure loss of exhaust gas can be avoided at a high engine speed, damping effect covering entire sound range as in the multistage-expansion type cannot be obtained and noise of specific frequency can only be reduced by the resonant effect.
Further, since the control valve is used, a movable portion is required in a high-temperature portion, thus lacking reliability.